Converting photographic images into color



Patented May 25, 1943 Percy D. Brewster, Holmdel, N. J.

CONVERTING PHOTOGRAPHIC IMAGES INTO COLOR No Drawing. Application July 3, 1940, Serial No. 343,747

7 Claims.

Thi invention relates to color photography, more particularly to the converting of silver photographic images carried by a gelatin coating on a suitable support into a dye mordant, which, when treated with the proper dyes forms images in color.

The chief object of the invention, stated gen- I erally, is the conversion of positive silver images, printed from a negative, into a silver iodide mordant of adequate dye-absorptive power which is relatively or totally transparent'to transmitted colloid or gel form of silver iodide. To these and other ends my invention comprises the novel features hereinafter described.

' talloid and colloid forms of silver iodide.

Silver iodide mordantshave been formed by several different methods producing different types of. mordant, each having well defined characteristics, for example; Traube in United States Patent No. 1,093,503, dated April 14, 1914, hereinafter referred to as the Traube type, produces a translucent white or yellowish-white mordant that absorbs dye very slowly to produce dull images, unsuited for modern color cinematography, but which reproduces the negative image grain or grain complexes with extreme accuracy.

Miller ill United States Patent No. 1,214,940 dated February 6, 1917, hereinafter referred to as the Miller type, produces, under proper processingconditions, a mordant that is absolutely transparent to the eye to transmitted light and that adsorbs dye strongly and quickly to produce brilliant images-but reproduces the negative image grain or grain complexes comparatively poorly, especially in the highlights. In my United States Patent No. 1,992,169 dated February 26, 1935, hereinafter referred to as "1935, Brewster type, I formed the mordant by action of a gaseous acid producing a mordant, which, under proper processing, produces a transparent mordant which adsorbs dye quickly to produce a brilliant image closely resembling the Miller process mordant but reproducing the negative image grain or grain complexes much more sharply though probably not equalling the sharpness of the Traube process.

If the Traube type" mordant is formed, as is usual, without using one of the metallic salts of the iodides in the reaction, I believe to the best of my present chemical knowledge, the mordant formedis a pure crystalloid consisting of silver iodide. The Miller type mordant, formed under ideal conditions is fully transparent and probably is a colloid, the gel of silver iodide, but if the mordant is of the thin whitish translucent type, I believe it consists of a mixture of the crys- The mordant formed by the 1935 Brewster type under ideal conditions is transparent, adsorbs dye very well and produces sharp images but, in practise, requires a careful control of the pH of the soak solution to produce even results over long lengths of film and is not adapted for the production of a heavy translucent mordant to yield dull color images or sound track;

This invention, in 'generalcomprises impregnating the gelatin'coating bearing silver images, with a solvent for iodine or other suitable bleach and then subjecting the impregnated coating to iodine or other suitable bleach in gaseous or vapor form. Solvents may consist of iodides such as potassium or sodium iodide or glacial acetic acid or certain alcohols diluted with water. The

efiectiveness of many of these -solvents may be increased if the solvent is acidified. The bleach may be iodine vapor or gas containing iodine vapor or hydriodic acid in gaseous form: The mordant so formed in the gelatin may be treated with a reducing agent forexample: a two percent solution of sodium-bisulphite to clear it of excess iodine and may then be dyed in the usual manner.

For most purposes in color cinematography, except production of sound track, I prefer to form a mordant which is transparent or which has only a thick, whitish, translucent ghost image which absorbs dye strongly and quicklyv and which when dyed reproduces the silver image grains or grain complexes with the greatest accuracy.

To accomplish this I prefer to use iodine vapor at a temperature not much above room temperature and a solvent impregnated in the gelatin coating which not only freely dissolves the iodine vapor but has a strong tendency to form a colloidalgel of silver iodide. The metallic salts of the iodides possess this quality, especially po tassium iodide, which I prefer to use for the sol-' vent in a relatively weak solution. Lbelieve, to the best of my present chemical knowledge,.that transparent colloidal silver iodide mols, especially those forming the. weak portions of the image, are dissolved by the action of strong iodides used as solvents within the gelatin causing the sharp outlines of the silver image grain complexes to be dissolved out or causing them to diffuse resulting in loss of definition of the mordant image. For example, using hardened gelatin, to 8% solutions of potassium iodide have little or no solvent action on the silver image or mordant in the short time the solvent is necessarily in contact with the mordants but if stronger potassium iodide is usedit is possible under certain conditions, that the sharpness of the images may be affected.

It is impossible to offer a fixed formula for bleaching or converting the silver image into a mordant adapted for coler cinematographic use contrast or gamma and which has been hardened.

in 9. formaldehyde solutionand dried without rinsing, though good results can be obtained on unhardened film.

a At present I prefer, in the practise of my invention, to use iodine gas or vapor to convert the silver images into dye mordants. Iodine vap01 is much heavier than air and is readily formed by placingiodine in a vessel or chamber and circulating air over it, the strength of the iodine vapor being largely controlled 'by the temperature of the air in contact with it. The

gelatin. coating, bearing the silver images to be bleached, may be impregnated with a l /2% solution, of potassium iodide, a. ten to thirty second immersion being usually suiiici-ent. The excess solution is removed from the gelatin surface by' The filmis then treated with the iodine gasin a chamber at a teman air blast or squeegee.

perature of about '73 degrees F. until the silver images are converted or bleached into the mordant, and quickly cleared in 3% sodium bisulphite solution and rinsed. The time of bleaching may vary from thirty to ninety seconds under ideal conditions. It is tobe understood that the concentration of the potassium iodide and iodine vapor and time of treatment may vary to any extent without departing from my invention. Speaking generally, if the iodine vapor is "too concentrated there is a tendency to bleach quickly and to form the Traube type of mor dant, whil too weak an iodine vapor may cause a. slow bleach which forms a whitish mordant that may not dye so well.

A weak potassium iodide solution has some advantages. It may not have sufilcient iodide pres- -ent to form the best colloidal mordant and may cause a. slow bleach, while too strong an iodide solution, to the best of my present knowledge, may have a solvent action on the mordant and Icause a loss of image sharpness. If the concenf tration of the iodide be sufliciently high, the gelatin, especially if it is nothardened, may be dissolved.-, Images can be bleached with a 1% solution of potassium iodide but the operation is slow and little advantage seems to be gained.

- If sound tracks are being colored orinten'sified I prefer a more opaque Traube type" image and do not require a gel forming salt or only a very small. amount of such salt in the solvent.

To form the opaque mordant of the "Traube type, I prefer to use a higher vapor pressure of iodine at a temperature of one hundred degrees F. or more in a combination with a solvent which is weak in iodide or contains no iodide at all. Such a combinatio produces an. extremely rapid bleach probably tending .to'reduce the formation of colloidor gel form of iodide and results in a. heavy mordant.

completely transparent mordant may be formed;

The hydrogen iodide gas maybe mixed with air or other gas to control the speed of the reaction. The alkali metal iodides such as ammonium or sodium iodide may be substituted for potassium iodide. Many of the metallic iodides such as cadmium iodide are solvents of iodine vapor and substantial loss of definition which comprises 'colloid forming salt is present.

cause the gelatin coating, when treated with iodine vapor, to be come discolored with the reddish brown iodine stains, but the penetration of the iodine into the gelatin isusually quite slow and an unsatisfactory mordant results unless a Impregnating the gelatin coating with a solvent is intended to mean thoroughly moistening but not necessarily saturating the gelatin with the solvent.

The solvent in the gelatin for iodine vapor does not imply any chemical reaction. However, when hydrogen iodide is used as a bleaching agent the acidified solvent causes free iodine to be liberated which may be dissolved and carried into the gelatin by the iodide present in the solvent which also results in the formation of a transparent gel mordant.

I claim:

1. Process for converting a silver photographic image carried in a gelatin coating on a, suitable support into a transparent dye mordant without substantial loss of definition which comprises impregnating said coating with a solvent for a gaseous bleach then treating said coating with said gaseous bleach.

2. Process for converting a silver photographic image carried in a gelatin coating on a suitable support into a transparent dye mordant without impregnating said coating with an acidified sol- I vent for a gaseous bleach then treating said coating with said gaseous bleach.

3. Process for converting a silver photographic image carried in a gelatin coating on a suitable support into a transparent dye mordant without substantial loss of definition which comprises impregnating said coating with a solvent for 10- dine vapor then treating said coating with gas containing iodine vapor.

4. Process for converting a silver photographic image carried in a gelatin coating on a. suitable support into a transparent dye mordant without substantial loss of definition which comprises impregnating said coating with a solution of potassium iodide and treating said coating with iodine vapor.

a 5. Process for converting a silver photographic image carried in a gelatin coating on a suitable s saacas 3 support into a transparent dye mordant without substantial Boss of definition which commises impregnating said coating with an acidified soivent for hydrogen iodide and treating said impregnated coating with gaseous hydrogen iodide.

6. Process for converting a silver photographic.

image carried in a gelatin coating on a suitable support into a transparent dye mordant without substantial loss of definition which comprises impregnating said coating with an acidified solution of potassium iodide and treating said impregnated coating with a gas containing hydro= gen iodide.

7. Process for converting a silver photographic image carried in a gelatin coating on a. suitable support into a dye mordant which comprises impregnating the said coating with an acidified solvent for a. gaseous bleach and treating said coating with said gaseous bleach and controlling the solvent and bleach so as to form {either a 10 transparent or opaque mordant.

PERCY D. BREWSTER. 

